EP0327132A2

EP0327132A2 - Image forming member drive device of an automatic drawing apparatus

Info

Publication number: EP0327132A2
Application number: EP89102040A
Authority: EP
Inventors: Masaki C/O Dainippon Screen Mfg. Co.Ltd. Yoshioka; Kenji C/O Dainippon Screen Mfg. Co.Ltd. Nakai; Kenji C/O Dainippon Screen Mfg. Co. Ltd. Watanabe; Takaharu C/O Dainippon Screen Mfg.Co.Ltd Yamamoto; Takeji C/O Dainippon Screen Mfg. Co.Ltd Hashimoto
Original assignee: Dainippon Screen Manufacturing Co Ltd
Current assignee: Dainippon Screen Manufacturing Co Ltd
Priority date: 1988-02-05
Filing date: 1989-02-06
Publication date: 1989-08-09
Also published as: EP0327132A3; US5042155A; JPH01200999A; JPH0761759B2

Abstract

In a control device of an improved image forming member drive device of an automatic drawing apparatus, the image forming member is controlled in two modes, i.e., a position control mode and a pressure control mode. In the position control mode, the image forming member is controlled in a closed loop upon receipt of a feedback signal of its position in the vertical direction. In the pressure control mode, the image forming member is controlled in an open loop. Accordingly, the image forming member is located accurately and at high speed at a prescribed stop position at the beginning of the drive.

Description

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a device for driving an image forming member (such as a pen or a clipping cutter) in an automatic drawing apparatus and particularly to an image forming member drive device of an automatic drawing apparatus for controlling a raised or lowered position of the image forming member or an image forming pressure.

Description of the Background Art

An image forming member drive device of an automatic drawing apparatus of interest to the present invention is disclosed for example in Japanese Utility Model Laying-Open No. 66534/1974 or Japanese Patent Laying-Open No. 148696/1984.
In both of the above indicated documents, the image forming member of the automatic drawing apparatus is coupled to a moving coil and it is driven vertically by control of a value of current flowing in the moving coil.
According to the above indicated first document, the value of the current flowing at the time of lowering or raising the image forming member of the automatic drawing apparatus, connected to the moving coil is controlled in the following manner. When a lowering speed of the image forming member is detected (by detection of a quantity of light and by differentiation of a signal of the detected light quantity according to that document), the value of current to flow in the coil is determined by subtraction of the value of current dependent on the lowering speed from a predetermined value of current to flow in the coil. In other words, the lowering speed of the image forming member is detected and the value of current is controlled so that the speed is equal to a predetermined value. Thus, closed loop control is carried out by detecting only the speed. As a result, the image forming member is soft-landed on a sheet for image formation.
According to the second document, the value of current flowing in the moving coil connected to the image forming member of the automatic drawing apparatus is controlled in an open loop by using a function generating circuit, so that the image forming member is raised or lowered. When the image forming member is to be lowered, it is first accelerated to be lowered. The lowering speed is decreased before the image forming member reaches the image formation surface and, after that, the image forming member is stopped. Then, the image forming member is accelerated a little so that it is soft-landed on the image formation sheet. After that, a predetermined pressure is applied to the image forming member so that an image is formed. The above mentioned soft-landing means a contact of the image forming member with the image formation sheet without causing any impact or damage thereto.
More specifically, the image forming member is lowered at high speed toward the image formation sheet so as to be close thereto and then it is soft-landed on the image formation sheet. As a result, any impact or damage on the image formation sheet which would be caused by the image forming member can be prevented and an image can be formed with fine traces on the image formation sheet.
Generally, in an automatic drawing apparatus, the image forming member needs to BE operated accurately and smoothly so that the image forming member can be prevented from causing any damage and an image is formed with fine traces. For those purposes, it is necessary to control accurately and smoothly a value of current flowing in the moving coil connected with the image forming member. This is because the image forming member is driven in proportion to the current flowing in the moving coil based on the Flemings's left-hand rule.
The automatic drawing apparatus of the above indicated first conventional example has a speed detector for detecting a speed of the image forming member but this detector detects only the lowering speed of the image forming member. The lowering speed of the image forming member is controlled according to the detected value so that the image forming member is soft-landed on the surface of the image formation sheet. This prior art example involves disadvantages as described below. There are possibilities that the lowering time or the landing point of the image forming member differs dependent on the distance from the image forming member to be lowered to the surface of the image formation sheet. Accordingly, the image forming member might collide with the image formation sheet or bound thereon. Consequently, the life of the image forming member would be considerably reduced or fine traces could not be given.
According to the above indicated second prior art example, the steps of raising and lowering the image forming member are controlled in an open loop. Accordingly, the stop position of the image forming member is not fixed stably compared with the closed loop control system. Consequently, the same disadvantages as in the case of the first example are involved. In order to eliminate such disadvantages, it is necessary to adjust a drive control device for each drawing apparatus and such adjustment requires a lot of labor.
In each of the two examples, current of a prescribed value is caused to flow in the moving coil after the image forming member has landed on the image formation sheet. As a result, the image forming member is pressed against the image formation sheet under a prescribed pressure. However, if a cutter knife is used as the image formation member and a peel off film is used as the image formation sheet, the below described problems occur. If the peel off film is to be cut by using the cutter knife, it is necessary to set the pressure of the knife for cutting to 10 to 20 grams. When the peel off film is cut with such a very weak pressure for image formation, the image forming member is affected by irregularities on the image formation table due to errors of finishing of the table. Accordingly, in an extreme case, the cutter knife will spring up and normal cutting will not be carried out.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to attain a stable landing of an image forming member of an image forming member drive device of an automatic drawing apparatus.
Another object of the present invention is to stably fix a position where an image forming member is to be stopped after the lowering speed thereof is reduced in an image forming member drive device of an automatic drawing apparatus.
Still another object of the present invention is to effect an easy adjustment of an image forming member drive device of an automatic drawing apparatus.
A further object of the present invention is to press an object with a desired pressure in an image forming member drive device of an automatic drawing apparatus.
A still further object of the present invention is to prevent influence of irregularities of the an image formation table when an image is formed with a very small pressure in an image forming member drive device of an automatic drawing apparatus.
In order to accomplish the above describe objects, an image forming member drive device of an automatic drawing apparatus according to the present invention includes: a table on which an object of image formation is to be placed; an image forming member provided over the table, for forming an image on the object ; a vertical drive device connected to the image forming member, for driving the image forming member vertically; a position detector for detecting a vertical position of the image forming member; and a position controller for controlling the vertical position of the image forming member in response to an output signal of the position detector.
The image forming member drive device of the automatic drawing apparatus according to the present invention is thus constructed. Consequently, the vertical position of the image forming member is detected and, in response to the detection signal, a closed loop circuit control is effected so that the image forming member stops at a prescribed position. As a result, the image forming member in the image forming member drive device of the automatic drawing apparatus can be landed stably.
According to a preferred embodiment of the invention, the vertical drive device for the image forming member includes: a first current generator for generating a first current in response to the output signal of the position detector, a first magnetic field generator connected to the image forming member, for generating a magnetic field in response to the first current, and a second magnetic field generator provided to guide the first magnetic field generator.
The image forming member is driven by mutual reaction of the magnetic fields generated by the first and second magnetic field generators.
According to a further preferred embodiment of the invention, since the image forming member drive device is thus constructed, the image forming member is driven only by controlling the current flowing in the first magnetic field generator and the driven amount is defined by the output signal of the position detector. Accordingly, in the image forming member drive device, the position of the image forming member can be controlled easily.
According to a further preferred embodiment of the invention, the image forming member drive device further includes a pressure signal output device for outputting a pressure signal for pressing the object on the table, a second current generator for generating a second current in response to the pressure signal, a third magnetic field generator connected to the image forming member, for generating a magnetic field in response to the second current, and a fourth magnetic field generator provided to guide the third magnetic filed generator, and the image forming member presses the object by mutual reaction of the magnetic fields generated by the third and fourth magnetic field generators.
According to a further preferred embodiment of the invention, the image forming member drive device is thus constructed and, accordingly, a pressure signal and a pressing force corresponding thereto can be easily obtained. As a result, in the image forming member drive device, the object can be pressed with a desired pressing force by controlling the pressure signal.
According to a further preferred embodiment of the invention, the vertical drive device for the image forming member further includes a damping device for damping the contact of the image forming member with the object of image formation.
Since the image forming member drive device is thus constructed, the impact force is relieved even if the image forming member contacts the image formation table abruptly. Accordingly, in the image forming member drive device, even if an image is formed with a very small pressure, the image forming member is not affected by the irregularities of the image formation table.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a perspective view of an image forming head of an image forming member drive device according to the present invention.
Fig. 2 is a sectional view of the image forming head.
Fig. 3 is a block diagram showing control relations of the image forming member drive device according to the present invention.
Fig. 4 is a diagram showing an example of control of an image forming member drive device of an automatic drawing apparatus according to the present invention.
Fig. 5 is a graph for explaining a relation between a current value of a coil connected to the image forming member and a lowered position of the image forming member corresponding thereto.
Fig. 6 is graph showing a relation between a signal value corresponding to the position of the image forming member and a current corresponding value of a moving coil corresponding to the position.
Fig. 7 is a graph showing a relation between a pressure value when the image forming member presses the image formation table and a current value in the moving coil.
Fig. 8 is a circuit diagram of a main part of an example of a damping circuit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Fig. 1 is a perspective view showing an image forming head to which an image forming member drive device according to the present invention is applied, and portions related thereto. Referring to Fig. 1, an automatic drawing apparatus including the image forming member drive device according to the present invention comprises an image formation table 1, an image forming head 10 for image formation on an image formation sheet 1a placed on the image formation table 1, a support 2 for supporting the image forming head 10, and an image forming kit 3 provided detachably on the support 2, for holding a plurality of pens 4 selectively used by the image forming head 10.
When image formation is effected, the image forming head 10 is supported by the support 2 and is moved to a desired position. When the pen attached to the image forming head 10 is to be replaced, another pen 4 held in the image forming kit 3 is attached to the image forming head 10 in place thereof.
Fig. 2 is a sectional view of a main part of the image forming head 10 shown in Fig. 1. Referring to Fig. 2, the image forming head 10 to which the present invention is applied comprises an image forming member 14, a drive portion 71 for driving the image forming member 14 vertically, and a support portion 72 for supporting the drive portion 71 movable in the vertical direction. The drive portion 71 comprises a coupling shaft 13 for supporting the image forming member 14, a moving coil 12 connected to the coupling shaft 13, and a permanent magnet 11 for driving the moving coil 12. The support portion 72 comprises a support bracket 15 for supporting the coupling shaft 13 movably in the vertical direction and rotatably in the horizontal direction, a support spring 16 for elastically supporting a movable portion including the moving coil 12, the coupling shaft 13 and the image forming member 14, a cylindrical shaft 17 provided in the support bracket 15 and located rotatably around the coupling shaft 13, and guide rollers 18 for supporting the coupling shaft 13 movably in the vertical direction.
An image forming member rotation drive portion 73 comprises a drive motor 20 for driving and rotating the image forming member 14, a drive pulley 21 provided at an output shaft of the drive motor 20, for transmitting an output of the drive motor 20, a transmission pulley 23 for rotating the coupling shaft 13, a transmission endless belt 22 engaged with the drive pulley 21 and the transmission pulley 23, for transmitting the driving force of the drive motor 20 to the coupling shaft 13, a rotation point detector 26 for detecting rotation of a rotating member 25 provided on the cylindrical shaft 17, and a rotation position detector 26a connected to the drive motor 20 for detecting a rotation position of the drive motor 20. A vertical position detecting portion 74 for detecting a vertical position of the image forming member 14 is provided on the support 2. The vertical position detecting portion 74 includes a slit plate 28 to be detected, provided on a bobbin support 12a of the moving coil 12, and a vertical position detector 40 for detecting a position of the slit plate 28. The vertical position detector 40 is formed by an infrared light emitting diode and a photodiode.
Referring to Figs. 1 and 2, operation of the image forming head 10 will be briefly described. When a signal instructing image formation is provided from a control device of the image forming member drive device to be described in detail afterwards, the image forming head 10 is moved to a predetermined position. At first, the image forming member 14 is positioned over the image formation sheet 1a. In response to an image formation signal, current flows in the moving coil 12 of the drive portion 71. As a result, the moving coil 12 is driven downward. In consequence, the image forming member 14 is driven downward and it stops at a predetermined position above the image formation table 1. The image forming member 14 is biased upward inherently by the support spring 16 through the coupling shaft 13. Accordingly, when the moving coil 12 is driven downward, the image forming member 14 is driven downward repulsively to the reaction force of the support spring 16.
After the image forming member 14 contacts the image formation sheet 1a, the permanent magnet 11 drives the moving coil downward so that the image formation sheet 1a is pressed by the image forming member 14 with a prescribed force.
Fig. 3 is a functional block diagram showing an operation principle of a control portion for controlling the drive portion 71 of the image forming head according to the present invention. Referring to Fig. 3, the control portion according to the invention moves the image forming member 14 when a predetermined current flows in the moving coil 12 of the image forming head and detects the position of the moved image forming member 14. The control portion further includes a current value control circuit 30 for providing a feedback signal based on the detection signal of the position of the image forming member 14 to position the image forming member 14 reliably. The control portion further includes a pressing force control circuit 70 which stores a relation between a pressing force applied to the object 1a of image formation and a value of current flowing in the moving coil 12 after the image forming member 14 contacts the object 1a and controls the pressing force of the image forming member 14 in an open loop by causing a current of a predetermined value to flow in the moving coil 12 of the image forming head according to the stored value.
The current value control circuit 30 comprises a position instructing circuit 33 for instructing the raised or lowered position of the image forming member 14 based on preset procedures, a pressure instructing circuit 34 for instructing a pressure for image formation of the image forming member 14, a current value output circuit 35 for outputting a necessary coil current value based on the instruction signals from the two instructing circuits, a position detecting circuit 41 for detecting the raised or lowered position of the image forming member 14, and a position correcting circuit 42. A closed loop control circuit is formed by the position detecting circuit 41, the position instructing circuit 33, the position correcting circuit 42 and the current value output circuit 35 until the image forming member 14 attains the prescribed stop position.
The pressing force control circuit 70 comprises a current value detecting circuit 45 for detecting the value of current flowing in the moving coil 12 of the image forming head in response to the pressure for image formation outputted from the pressure instructing circuit 34, a nonvolatile memory circuit 47 for storing in advance a relation between the pressure for image formation instructed by the pressure instructing circuit 34 and the value of the current flowing in the moving coil 12 at that time, and an evaluation circuit 51 for evaluating a value of current to flow in the moving coil 12 of the image forming head based on the data stored in the nonvolatile memory circuit 47. When the pressure for image formation with respect to the object 1a of image formation is instructed by the pressure instructing circuit 34, the pressing force applied to the object 1a by the image forming member 14 is controlled in an open loop based on the relation between the pressure and the value of current flowing in the moving coil, stored in advance in the nonvolatile memory device 47.
Thus, the functional block diagram was described by using the circuit diagram which represents the principle for controlling the drive portion 71 of the image forming head according to the invention. In the following, an embodiment of the image forming member drive device of the automatic drawing apparatus using this principle will be described.
Fig. 4 is a diagram showing the embodiment of the image forming member drive device controller based on the principle shown in Fig. 3. Referring to Fig. 4, the image forming member drive device controller according to the present invention comprises a control portion 32 for generally controlling the drive of the image forming member 14, an input device 31 connected to the control portion 32 through a data bus DB, a D/A converter 36 connected to the data bus DB, for converting an output signal from the control portion 32 to an analogue signal, an output mode switching circuit 38 formed by an analogue switch for switching an output mode according to the signal of the control portion 32, an output amplifier 37 connected to the output mode switching circuit 38, a damping circuit 53 connected to the output amplifier 37 for suppressing vertical movement of the image forming member 14, a current value detecting circuit 45 for detecting current flowing in the moving coil 12 connected to the image forming member 14, an input mode selection circuit 48 connected to the current value detecting circuit 45, for selectively inputting any of signals from the position detecting circuit 41 which detects the value of current flowing in the moving coil 12 or detects the vertical direction of the image forming member 14, an A/D converter 46 connected to the input mode selection circuit 48, for converting a signal inputted to the input mode selection circuit 48 to a digital signal and inputting the same to the data bus to input it in the control portion 32, a position differentiation output circuit 43 connected to the position detecting circuit 41, for showing down the raising or lowering speed of the moving coil 12, a position correcting circuit 42 connected to the position differentiation output circuit 43, the D/A converter 36 and the output mode switching circuit 38, and a nonvolatile memory circuit 47 connected to the control portion 32 through the data bus DB, for storing a position current correspoding value table T1 described in detail afterwards and a pressure current corresponding value table T2.
The control portion 32 is formed by a microcomputer and it comprises a CPU 32a, a ROM 32b, a RAM 32c, a position instructing portion 33 for instructing a position of the image forming member 14 connected to the CPU 32a or the like through the data bus DB, a pressure instructing portion 34 for instructing a pressure applied to the image formation table of the image forming member 14, and an evaluation portion 51 for evaluating a pressure corresponding value at the time of switching the output mode.
The position instructing portion 33 outputs a position instructing signal A based on a program stored in advance in the ROM 32b (for example concerning a change of current value according to the coil current (I) represented by Ia and Ib shown in Fig. 5, which will be described later) so as to control the lowered position of the image forming member 14.
The pressure instructing portion 34 outputs a pressure instructing signal K in a pressure control mode M2 described later, so that image formation is effected with the designated pressure P1 inputted through the input device 31.
The current output circuit 35 outputs a necessary coil current value I upon receipt of the instruction signals J and K from the position instructing portion 33 and the pressure instructing portion 34, respectively. The D/A converter 36 is controlled by an 8-bit signal and the raised or lowered position of the image forming member 14 is controlled by every 30 µm. If the image forming member 14 is a cutter knife, it is controlled with a resolution having a cutting pressure of several grams.
The output mode switching circuit 38 is formed by an analogue switch and it switches the output mode to a pressure control mode M2 upon determination that the image forming member 14 attains a decelerated lowered position C shown in Fig. 5 after a prescribed time after a signal level from the D/A converter 36 reaches a preset signal level.
The position detecting circuit 41 outputs the current value outputted from the raised or lowered position detector 40 shown in Fig. 2 as a signal corresponding to the raised or lowered position of the image forming member 14 in the form of an analogue amount.
The position correction circuit 42 is formed by an error amplifier and it compares the output signal from the position detecting circuit 41 with the level of the position instructing signal from the D/A converter 36 and outputs an error signal to the output mode switching circuit 38. The position detecting circuit 41 is provided with a position differentiation output circuit 43 for damping the raising or lowering speed of the moving coil 12, so that the output signal therefrom is inputted to the error amplifier 42.
The nonvolatile memory circuit 47 sets and stores the position current corresponding value and the pressure current corresponding value described later as data tables. This circuit 47 is formed by an EEPROM (Electrically Erasable and Programable Read Only Memory).
The input mode selecting circuit 48 is formed by an analogue switch and it sets and inputs data tables T1 and T2 described below into the nonvolatile memory circuit 47.
The data set in the data tables T1 and T2 are inputted to the nonvolatile memory circuit 47 through the 8-bit A/D converter 46.
Referring to Fig. 4, in the position control mode M1, a closed loop control circuit is formed by the position detecting circuit 41, the position instructing portion 33, the position correction circuit 42 and the current value output circuit 35 and the lowering operation of the image forming member 14 is controlled as shown by A to C in Fig. 4. In order to execute the control, the coil current value I is controlled as Ia to Ib based on the preset program.
Referring now to Fig. 5, description is made of a relation between the value of current flowing in the moving coil 12 of the image forming member 14 and the position of the image forming member 14 controlled thereby.
Referring to Fig. 5, the control device of the image forming member drive device of the automatic drawing apparatus according to the present invention has two modes, i.e., the position control mode M1 and the pressure control mode M2. In the position control mode M1, a closed loop circuit is formed in which the position of the image forming member 14 is detected and the signal is fed back to control the position. In the pressure control mode M2 for controlling the pressing force applied to the image formation sheet by the image forming member 14, an open loop control based on control of the current value of the moving coil is effected.
Referring to the left side of the graph of Fig. 5, description is made of the coil current I of the moving coil 12 in the position control mode M1 and the positional relation of the image forming member 14 corresponding thereto. The image forming member 14 is maintained at an initial position A (i.e., a state supported by the elastic spring 16) before turn-on of the power supply. Then, the image forming member 14 is lowered at high speed to a waiting position B after the turn-on of the power supply. Subsequently, the image forming member 14 is accelerated and lowered upon receipt of the image formation start signal and before it reaches the surface of the image formation sheet 1a, it is temporarily decelerated and stopped. The stop position C after the deceleration is set to a value so that the tip of the cutter knife 14 is maintained at a position of about 0.8 mm above the surface of image formation for example.
The current value I is defined by detecting the value of current flowing in a resistance for current detection shown in Fig. 4 by the current detecting circuit 45.
As described above, according to the present invention, the closed loop circuit is formed and the coil current value is controlled in the position control mode M1 until the image forming member 14 is decelerated and stopped. Consequently, the image forming member 14 is positioned at high speed and accurately at the stop position C. After that, the open loop circuit is formed and the coil current value is controlled in the pressure control mode M2. Since the stop position C is selected as a position close to the image formation sheet, the image forming member 14 can be landed smoothly and stably on the image formation sheet.
Next, setting and inputting of the data tables will be described.
Fig. 6 is a graph showing a relation between the moving distance (corresponding to raised or lowered position) of the image forming member 14 and the current value of the moving coil 12, that is, the position current corresponding value table T1. This data table T1 is set and inputted to the nonvolatile memory circuit 47 in the following manner.
First, a position input mode is selected by the mode selector of the input device 31. Then, the output mode switching circuit 38 sets the position control mode M1 and the other input mode selection circuit 48 sets the current value input mode. As a result, a closed loop control circuit is formed by the control portion 32, the D/A converter 36, the error amplifier 42, the output mode switching circuit 38, the output amplifier 37 and the position detecting circuit 41, while a learning circuit is formed by the current value detecting circuit 45, the input mode selection circuit 48, the A/D converter 46 and the nonvolatile memory circuit 47.
Next, the signal level (position corresponding value V_H) from the D/A converter 36 increments by one from 0 in response to the instruction signal from the position instructing portion 33 of the control portion 32. In response thereto, the moving coil 12 is lowered repulsively to the support spring 16. The current value of the moving coil 12 at this time is read as the current corresponding value I_H through the A/D converter 46. Learning is effected by executing this procedure for all the stroke of raising and lowering the image forming member 14. As a result, the position current corresponding value table T1 is inputted to the nonvolatile memory circuit 47.
Referring now to the right of Fig. 5 showing the coil current I in the pressure control mode M2 and the position of the image forming member 14, and to Fig. 7 showing the pressure current corresponding value table T2, pressure control of the image forming member 14 in the pressure control mode M2 will be described.
Fig. 7 is a graph showing the relation between the pressure P of image formation of the image forming member 14 and the current value of the moving coil 12, that is, the pressure current corresponding value table T2. This data table T2 is inputted to the nonvolatile memory circuit 47 in the following manner.
The pressure input mode is selected by the mode selector provided in the input device in the same manner as described previously. The output mode switching circuit sets the pressure control mode M2 and the other input mode selection circuit 48 maintains the current value input mode. Then, a learning circuit is formed by the control portion 32, the D/A converter 36, the output mode switching circuit 38, the output amplifier 37, the current value detection circuit 45, the input mode selection circuit 48, the A/D converter 46 and the nonvolatile memory circuit 47.
Subsequently, in response to the instruction signal from the pressure instructing portion 34, the level (the pressure corresponding value V_P) of the output signal from the D/A converter 36 increments by one from 0 in the same manner as described previously. In response thereto, the pressure of image formation of the moving coil 12 increases. The coil current value at this time is read as the current corresponding value I_P through the A/D converter 46. The relation between the pressure corresponding value V_P and the current corresponding value I_P is learned until the pressure corresponding value V_P attains the maximum value 256 represented by 8 bits. As a result, the pressure current corresponding value table T2 is inputted to the nonvolatile memory circuit 47.
If a plural number of such tables T2 (for example, for low pressure, medium pressure and high pressure) are prepared by changing the gain of the output amplifier 37, the table T2 can be suitably utilized according to the purposes such as cutting or marking off. Before the tables T2 are prepared, the gain of the output amplifier 37 is finely adjusted so that the output of the pressure indicator 27 (a shown in Fig. 4) with the maximum pressure corresponding value V_P is a reference pressure value P_X. In the case of cutting, the table T2 is prepared so that the peel off film is cut with a pressure of about 10 g to 20 g. Thus, the input mode is terminated.
The evaluation portion 51 performs evaluation as described below with reference to the data tables T1 and T2 learned as described above, so that the value I of current flowing into the moving coil 12 at the time of switching of the output control mode from the position control mode M1 to the pressure control mode M2 may not jump or may not be discontinuous.
When the image forming member 14 reaches the stop position C in Fig. 5, that is, at the end of the position control mode M1, a required current corresponding value I₀ is calculated with reference to the data table T1 based on the position instruction from the position instructing circuit 33. Then, based on the current corresponding value I₀, a required specified pressure corresponding value V0 is calculated with reference to the table T2 based on the current corresponding value I0. This specified pressure corresponding value V0 corresponds to a signal level equivalent to the pressure P0 required for maintaining the image forming member 14 at the stop position C repulsive to the support spring 16.
On the other hand, the designated pressure P1 of image formation preset in the input device 31, the pressure corresponding value V1 corresponding thereto is calculated with reference to the data table T2. This pressure corresponding value V1 and the above mentioned specified pressure corresponding value V0 are added and the added pressure corresponding value V2 is outputted to the pressure instructing portion 34. Thus, the evaluation is completed.
After an elapse of a predetermined time (t) after the image forming member 14 attains the stop position C, an output mode switching signal is provided from the CPU 32a so that switching is effected by the output mode switching circuit 38 from the position control mode M1 to the pressure control mode M2. At this time, the current corresponding value for the moving coil 12 is maintained at the fixed value I0 irrespective of before or after the switching of the control mode. Accordingly, there is no fear of vertical fluctuation of the image forming member 14 or erroneous setting of its height.
After that, the current corresponding value for the moving coil 12 increase gradually until it attains the current corresponding value I2 corresponding to the above mentioned added pressure corresponding value V2 inputted to the pressure instructing circuit 34. As a result, the image forming member 14 gradually lowers from the temporary stop position C and is soft-landed on the surface of the image formation sheet 1a. On this occasion, the pressure applied to the image forming member 14 increases gradually until it changes from 0 to the designated pressure P1 for image formation. After the image forming member 14 reaches the soft-landing point D, image formation is effected with the prescribed designated pressure P1 of image formation.
As described above, in the preferred embodiment of the invention, corresponding values between the position and current of the moving coil 12 and between the power and the current are stored as data tables in advance into the nonvolatile memory circuit 47 through the learning circuit at the stage of adjustment of the image forming member drive device. When switching is made from the position control mode M1 to the pressure control mode M2, the above mentioned data tables are referred to through the evaluation portion 51 and the specified pressure corresponding value V0 of the image forming member 14 and the required image formation pressure corresponding value V1 are calculated so that those values are added to obtain the added output corresponding value V2.
The specified pressure corresponding value V0 corresponds to the signal level equivalent to the pressure P0 required for maintaining the image forming member 14 at the above mentioned stop position C repulsive to the entire support system including the moving coil, the coupling shaft and the image forming member. The prescribed image formation pressure corresponding value V1 corresponds to the signal level equivalent to the pressure P1 required for image formation in the above mentioned maintained state.
The coil current value is controlled through the pressure instructing circuit 34 and the current value output circuit 35 based on the above mentioned specified pressure corresponding value V0 and added pressure corresponding value V2. When the image forming member 14 moves from the stop position C and is soft-landed, the image formation pressure increases from 0 to the prescribed image formation pressure P1. As a result, even if the characteristics of the entire support system for the image forming member, the position detector, the output amplifier and the like differ for each apparatus, individual fine adjustment is not required. Particularly, at the time of switching of the output mode, the image forming member does not sway or is not unstable and thus the image forming member is controlled smoothly.
Next, a further preferred embodiment of the invention will be described. In this embodiment, the image forming member drive device includes a damping circuit 53 as shown in Fig. 3.
The damping circuit 53 is effectively utilized in the case of cutting a peel off film using a cutter knife as the image forming member for example when the cutter knife is caused to run with a very small pressure. More specifically, when the cutter knife is caused to run with a very small pressure, the cutter knife might spring up due to irreguralrities caused by the error of lowering on the image formation table. Therefore, in order to avoid this, the damping circuit 53 is provided, which comprises a resistance circuit where a resistance value can be adjusted. More specifically, in the damping circuit 53, the output impedance of the output amplifier 37 is set to a sufficient low value so that current caused by counter-electromotive force of the moving coil 12 is controlled. As a result, the cutter knife 14 can be prevented from springing up.
Fig. 8 is a circuit diagram showing a variant of the damping circuit 53. Referring to Fig. 8, a series damping circuit is provided which comprises a resistor 52a and a capacitor 52b in parallel with the moving coil 12, and, in such a case, the same effect can be obtained. In this case, only a high-frequency component of the counter-electromotive force is absorbed. Accordingly, the cutter knife 14 runs along the irregularities on the image forming table.
The present invention is not limited to the above described embodiments and it goes without saying that various variants may be adopted.
As is understood from the foregoing, according to the present invention, the closed loop circuit is formed and the coil current value is controlled in the position control mode until the image forming head attains the stop position. Accordingly, the image forming member can be soft-landed smoothly and stably compared with the convention image forming member drive control devices.
According to the first preferred embodiment, fluctuation of the coil current value can be prevented based on the data tables learned in advance, when the output mode switches from the position control mode based on the closed loop to the pressure control mode based on the open loop. As a result, it is not necessary to take any account of irregularities in characteristics of the elements of the support system and the control circuit at the stop position of the image forming member while maintaining stability at the stop position. Accordingly, the control device for the whole drive device can be adjusted easily.
According to the second preferred embodiment, the damping circuit of the simple construction is provided in the control circuit of the image forming member drive device and accordingly the stable running of the image forming member is ensured without being affected by any irregularities on the image formation table.
Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.
The features disclosed in the foregoing description, in the claims and/or in the accompanying drawings may, both, separate]y and in any combination thereof, be material for realising the invention in diverse forms thereof.

Claims

1. An image forming means drive device comprising:
means for placing an object of image formation,
image forming means provided over said placing means, for forming an image on said object,
image forming means drive means connected to said image forming means, for driving said image forming means vertically,
position detecting means for detecting a vertical position of said image forming means, and
position control means for controlling the vertical position of said image forming means in response to an output of said position detecting means.

2. An image forming means drive device in accordance with claim 1, wherein
said image forming means drive means comprises
first current generating means for generating a first current in response to the output signal of said position detecting means,
first magnetic field generating means connected to said image forming means, for generating a magnetic field responsive to said first current, and
second magnetic filed generating means provided to guide said first magnetic filed generating means,
said image forming means being driven by mutual reaction of the magnetic fields generated by said first and second magnetic field generating means.

3. An image forming means drive device in accordance with claim 2, wherein
said first magnetic field generating means generates a first magnetic field proportional to said first current.

4. An image forming means drive device in accordance with claim 3, wherein
said first magnetic field generating means includes an electromagnetic coil, and
said second magnetic field generating means includes a permanent magnet.

5. An image forming means drive device in accordance with claim 4, wherein
said position control means includes first current value detecting means for detecting a value of said first current.

6. An image forming means drive device in accordance with claim 5, wherein
said drive device further includes first storing means, and
said first storing means stores a relation between the vertical position of said image forming means and the value of the first current corresponding to said vertical position.

7. An image forming means drive device in accordance with claim 6, wherein
said drive device further includes first input means, and
said first input means includes operation mode selecting means for selecting an operation mode of said image forming means drive device.

8. An image forming means drive device in accordance with claim 7, wherein
said operation mode includes a position control mode for controlling a position of said image forming means.

9. An image forming means drive device in accordance with claim 1, wherein
said drive device further includes pressure signal output means for outputting a pressure signal for pressing said object on said placing means,
said image forming means drive means includes
second current generating means for generating a second current in response to said pressure signal,
third magnetic field generating means connected to said image forming means, for generating a magnetic field responsive to said second current, and
fourth magnetic field generating means provided to guide said third magnetic field generating means, and
said image forming means presses said object by mutual reaction of the magnetic fields generated by said third and fourth magnetic field generating means.

10. An image forming means drive device in accordance with claim 9, wherein
said third magnetic field generating means generates a second magnetic field proportional to said second current.

11. An image forming means drive device in accordance with claim 10, wherein
said third magnetic field generating means includes an electromagnetic coil, and
said fourth magnetic field generating means includes a permanent magnet.

12. An image forming means drive device in accordance with claim 11, wherein
said position control means includes second current value detecting means for detecting a value of said second current.

13. An image forming means drive device in accordance with claim 12, wherein
said drive device further includes second storing means, and
said second storing means stores a relation between a pressing force corresponding to said pressure signal and the value of said second current corresponding to said pressing force.

14. An image forming means drive device in accordance with claim 13, wherein
said drive device further includes pressing force input means for inputting a desired pressing force for pressing said object, and
said image forming means drive means presses said object with said desired pressing force according to the relation between said pressing force and said second current value stored in said second storing means.

15. An image forming means drive device in accordance with claim 9, wherein
said image forming means drive means further includes damping means for damping contact of said image forming means with said object.

16. An image forming means drive device in accordance with claim 15, wherein
said damping means absorbs counter-electromotive force generated in said third magnetic filed generating means.

17. An image forming means drive device in accordance with claim 16, wherein
said damping means includes a series connection of resistance means and capacitance means connected in parallel with said third magnetic field generating means.